1.1. Measurements And Their Errors: Paper 1: Physics A Level AQA

What are SI units?

Fundamental (base) units of physical quantities.

What is the SI unit of mass?

kg (kilogram)

What physical quantity is measured in mol?

Amount of substance.

What is the SI unit of current?

A (Amperes)

Is the SI unit for temperature ℃ or K ?

K (kelvin) as this is the absolute scale.

What is the SI unit of length?

m (metres)

What quantity is measured in seconds?

Time

Are Newtons (N) an SI unit?

No, newtons are not fundamental, the SI units for force are kg⋅m⋅s^-2.

Derive the SI units of energy.

Kinetic energy = ½ x mass x velocity squared

Units = kg x (m/s) x (m/s)

Units = kg⋅m^2⋅s^-2

Derive the SI units of force.

Force = mass x acceleration

Units = kg⋅m⋅s^-2

Units = kg⋅m/s^-2

Express 60 TΩ in standard form.

6 x 10^13

(T is tera and the multiplier is 10^12)

Write 0.000003m with a suitable prefix.

3 μm

What is the actual value of 8MΩ?

8,000,000 Ω or 8x10^6 Ω

What is 6000pF in nF?

6 nF as 1 nano unit is 1,000 pico units.

What multiplier is associated with the prefix kilo (k)?

1000 (10^3)

What multiplier is associated with the prefix femto (f)?

10^-15

Express 7GΩ is standard form.

7 x 10^9 Ω

What is 1 eV in J?

1 eV = 1.6 x 10^-19 J

Express 6 kWh in joules.

6 kW = 6,000 J/s

1 hr = 3,600 s

6 kWh = 6,000 x 3,600

6 kWh = 21.6 x 10^6 J

6 kWh = 21.6 MJ

Convert 6.6 pJ to eV.

6.6 pJ = 6.6 x 10^-12 J

Divide by 1.6 x 10^-19

6.6 pJ = 4.1 x 10^7 eV (2 sf)

6.6 pJ = 41 MeV

What is a random error?

An error that affects precision and cannot be completely removed, it causes differences in measurements.

What is a systematic error?

An error that affects accuracy and occurs due to faults in equipment or experimental method, causing the result to be too large / small by the same amount each time.

What are 3 ways to reduce random error?

● Take at least 3 repeats and calculate a mean.

● Use a computer or a data logger.

● Use higher resolution equipment.

A mass balance reads 1,004 g when a 1 kg mass is placed on it, is this a

random or systematic error?

Systematic as the reading is too high by 4 g each time.

State a cause of parallax error.

Reading a scale at a different angle each time, to correct this you should read scales at eye level to reduce parallax error.

How can systematic error be reduced?

Calibrate apparatus before using e.g. zero the balance when it is empty.

Is electronic noise in the circuit of an ammeter random error or systematic error?

It is a random error as it will cause fluctuations in readings that affect precision and it cannot be removed.

Why should you measure background radiation before measuring the radioactivity of a source?

So that only the source’s radioactivity is measured, by accounting for background radiation systematic error is reduced.

What is precision?

Precise measurements are consistent, they fluctuate slightly about a mean value - this doesn’t indicate the value is accurate.

What is repeatability?

If the original experimenter can redo the experiment with the same equipment and method then get the same results it is repeatable.

What is reproducibility?

If the experiment is redone by a different person or with different techniques and equipment and the same results are found, it is repeatable.

What is meant by resolution?

The smallest change in the quantity being measured that gives a recognisable change in reading.

What is meant if a value is accurate?

If the value is close to the true value.

What is absolute uncertainty?

Uncertainty given as a fixed quantity e.g. 7 ± 0.6 V.

What is the percentage uncertainty in 17 ± 3 A?

3/17 x 100 = 17.647 % = 18 % (2 sf)

How can percentage and fractional uncertainty be reduced?

Measure larger quantities e.g. a longer rope will have a smaller percentage uncertainty than a shorter one.

What is the difference between a reading and a measurement?

Readings are when one value is found, measurements are when the difference between 2 readings is found.

What is the uncertainty of a thermometer whose smallest division is 5℃?

The uncertainty in a reading is ± half the smallest division, so the uncertainty is ± 5/2 or ± 2.5 ℃.

What is the uncertainty in the charge of an electron (1.6 x 10^-19 C)?

The uncertainty in a given value is ± the last significant digit: 1.6 x 10^-19 ± 0.1 x 10^-19 C

What is wrong with writing 7 ± 0.673 V?

The uncertainty should be the same number of significant figures as the data ie. 7 ± 0.7 V.

When drawing a line of best fit on a graph with error bars what must you do?

Make sure the line of best fit goes through all the error bars.

How do you find the uncertainty in the gradient of a line of best fit?

Draw a steepest or shallowest line of worst fit, it must go through all the error bars.

Calculate the gradient of the best and worst line, the uncertainty is the difference between the best and worst gradients.

What is an order of magnitude?

Powers of ten which describe the size of an object, and which can also be used to compare the sizes of objects.

What is the order of magnitude for the diameter of a nucleus?

10^-15

What is estimation?

A skill physicists must use in order to approximate the values of physical quantities, in order to make comparisons, or to check if a value they’ve calculated is reasonable.

What is 9.71 x 10^-21 to the nearest order of magnitude?

It is 1 x 10^-20 to 1 sf. So the nearest order of magnitude is 10^-20.